1. Field of the Invention
The present invention relates to a large wind turbine intended primarily to generate electricity for power plants. The purpose of the invention is to achieve the best possible benefit-to-cost ratio.
2. Prior art
This invention presents a new design and several essential improvements upon a known and tested type of vertical-axis wind turbine called cyclogyro or gyromill, as it is described in the book "Wind Power Plants--Theory And Design" by Desire Le Gourieres, Pergamon Press 1982, pages 143, 144, 177, 194 and 195. Cyclogyro is generally characterized by a vertical shaft carrying two sets of radially from the shaft connected horizontal struts, as cantilevers, one set above the other, straight vertically positioned blades which are pivotally attached each to a pair of said struts. It also has a tail or vane attached to a vertical axle, which axle is mounted in bearings on top of said turbine shaft by a short horizontal arm, so that said axle is positioned eccentrically to the turbine shaft, with steering rods to eccentric axle link following blades. Because said axle is carrying a vane which is always turned by the wind to lee side, trailing portion of each blade is pulled downwind positioning the blades pitch-angle in to the wind, which allowes this vertical-axis wind turbine to be self-starting and more efficient. By rotation of the turbine, the pitch-angle of each blade is cyclically changed from its maximum when speeds of the blade and of the wind are mutually perpendicular, to zero when those speeds are mutually parallel. Because of said cyclical changing of pitch-angle of each blade with each revolution of the rotor, this turbine is called cyclogyro. Cyclogyros however have some disadvantages common to verticals; blades have symmetric airfoils which are less efficient than asymmetric (cambered) blades used on horizontals, and pitch-angle of blades on cyclogyro is not adjustable to different wind speeds, because the pitch amplitude is determined by said eccentricity which is unchangeable. Besides, construction of such an eccentric axle, with a vane mounted on it, presents a very heavy load on its bearings. It is also exposed to extra wear and tear caused by gusts, as with other wind turbines, while solutions for horizontals, as e.g. "the teetering rotor", are not suitable for cyclogyro. Because of rotation on vertical axis, blades on cyclogyro are exposed to forces of wind on both sides alternatively, causing additional stress. This can be prevented with strut supports, which divide the blade in four shorter and much more durable sections as shown in the present invention. The blades of cyclogyro are also exposed to centrifugal force, but because this force diminish with added distance from center of rotation, however with larger turbines that force is a minor problem and can also be minimized by adding supports to the blades as in the present invention.
Cyclogyro was described in publications including Darrieus turbine, as one of the two most successful types of vertical-axis wind turbines. Presently only Darrieus turbine has remained in further experimentations, because of its low-cost design and simpler to manufacture, however not as efficient as herewith presented cyclogyro design. Through extensive search no cyclogyro wind turbine was found.
There are patented inventions of various vertical-axis wind turbines intended to achieve better efficiency or lower costs. Some are related to the present invention in attempt to solve the same problems in different ways, as in following patents:
In U.S. Pat. No. 5,252,029 to Barnes [November 1993] a way of assembling a turbine on ground level and to erect it by a winch is invented, but it was for another type of turbine, not suitable for a three-legged tower as in the present invention. PA1 In U.S. Pat. No. 4,383,801 to Pryor [May 1983] problem of pitch control is solved by three flanges which are as large as the turbine diameter, at a high cost for construction making this turbine not economically viable. PA1 In U.S. Pat. No. 5,193,978 to Gutierrez [March 1993] blades are pitched directly by relative fluid flow, without any other control, which is a system not comparable with the present invention. PA1 In U.S. Pat. No. 5,663,600 to Baek et al. [September 1997] a gear drive of sun-and-planet type was invented, but without possibility of changing speed ratio as it is possible in the present invention. PA1 In German patent application No. P-3816431.0 [Munich, May 13, 1988] inventor disclosed a way to utilize interpolated blade parts mounted on a special joint very similar to grease-box 39 in the pivotal blade-to-aileron link of the present invention. That solution has a significant disadvantage, which is eliminated in my invention. To allow contraction of distance between two secondary pivots on deviated aileron, one secondary pivot is inserted in a slot with straight walls, so that pivot-to-slot contact surfaces were extremely small, causing high stress on those surfaces. That causes rapid wear in connecting parts, creating excessive vibrations which adds to increased turbulence instead of smoothing the flow. In the present invention this problem is solved with addind a small insert installed inside the grease-box, assuring contact surfaces to be equal at both secondary pivots.
In this present invention, said grease-box has an additional function: It is limiting aileron deviation-angle for best lift-to-drag ratio, and is designed specifically for those advantages.
During search for prior art there was not found a constant-speed wind turbine with the same or similar system of variable blade pitch and camber control, and there was no improvement of blade airfoil profile as in the present invention, also no wind turbine to be mounted on a three-legged tower.